Is talent really in that short supply that acqui-hiring makes sense? Wouldn't Yahoo have been better off just paying a million dollars a year to each of the developers Ms Mayer managed to bring on board?
If not, the alternative seems to be that Yahoo is buying up companies for no reason. My guess would be that they've been buying companies on the off chance that those companies had something that would turn Yahoo around in an afternoon.
Yahoo is a desperate company, in search of a money making scheme. It understandable. It can't be easy to look at the competitors and realise that you're on the path to becoming the next MySpace.
Yahoo do a few things well, their mail has at least earlier been good, Yahoo Finance is a great service, but there's no profit to be made from either.
Pure email is not monetizable, but if they could tie in some unobtrusive freemium feature, there might be something in there. Remember that thread about commodity traders living on Yahoo IM? Surely some sort of IM/email mashup that could allow you to file and export messages could be popular.
Yahoo will run it self into the ground trying to revive the glory days of Yahoo being the front page of Internet for millions of people. Management will not settle for a smaller service company, for a few niche markets.
Go social like InvestingNote. Track user models against the markets and host competitions.
It might be really valuable to acquire a team of people, known to work / accomplish together. I think talent is not in short supply but god teams are hard to come by.
Also, the patents they acquire might be important in the long term too.